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STM32F446 PA5 output levels at high frequency

Question asked by waclawek.jan on Apr 25, 2016
Latest reply on Nov 8, 2017 by Dana Myers
This is one for the ST insiders.

On a Nucleo64 (SB21, SB29, SB44 all disconnected) with STM32F446, the PA5 pin has been configured as AF5 (SPI1_SCK/I2S1_CK), push-pull, OSPEEDR set to 0b11 (and later tried also 0b10), compensation cell tried both on and off, DAC at default (i.e. off). SPI1 set to RXONLY mode with clock set to PCLK/2, which should output cca 40MHz onto PA5. The waveform on PA5 is a cca 500mVp-p 40MHz wave riding on a cca +2V DC offset. Cutting down the speed to PCLK/4 results in sane cca 20MHz waveform. SPI1_SCK at a different pin works as expected at PCLK/2 too.

The STM32F446 datasheet (rev.5) lists PA5's type as "TC", with no explanation what TC might mean... But even then, Table 58. I/O AC characteristics does not indicate that any pin should behave differently as far as output high-speed capability goes.

Does PA5 have a different drive than other pins, or do I overlook something?

Thanks,

Jan Waclawek

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